The overall objective of the proposed research is to isolate and characterize a receptor for HIN-1 (High In Normal-1). HIN-1 is a putative tumor suppressor gene recently identified using SAGE (Serial Analysis of Gene Expression) to compare gene expression profiles in normal and DCIS (ductal carcinoma in-situ, an early-stage breast tumor) mammary epithelial cells. HIN-1 appears to be a novel cytokine that is significantly down-regulated in 94 percent of human breast carcinomas. The first specific aim of the proposed research is to identify a receptor for HIN-1 using an expression cloning technique. An expression library generated from HIN-1 responsive mammary epithelial cells will be screened with alkaline phosphatase-tagged HIN-1. Specific aim 2 of the proposed research is to (A) confirm that HIN-1 binds directly to the isolated receptor by performing a co-precipitation assay, and (B) determine the affinity of HIN-1 for the isolated receptor by performing whole cell binding analysis. Specific aim 3 is to determine distribution of the HIN-1 receptor in breast cancer cell lines and in normal versus DCIS mammary epithelium using real-time quantitative PCR and in-situ hybridization. Identification and characterization of a HIN-1 receptor is the first step necessary to begin characterization of HIN-1 signal reception and transduction, and these studies may further suggest how loss of this signal may contribute to breast tumor progression.